AOL has fired its chief technology officer and two of her colleagues following the embarrassing release of search data last month that could have allowed spammers and internet scammers to target 650,000 of the internet portal's customers, it emerged last night.

The company, owned by the media conglomerate Time Warner, is understood to have fired Maureen Govern, who has been its chief technology officer only since last September, following an internal investigation. She was in charge of the division responsible for the data that was released.

Two other AOL employees - a researcher and a manager - are also understood to be leaving as a result of the firestorm of criticism that hit AOL when the release of the data became public. The company was not immediately available for comment.

As an indication of the dismay with which the online search engine and portal giant greeted the news that some of its own data had been made available to everyone over the web, an AOL spokesman described it at the time as "a screw-up, and we're angry and upset".

The company's former chief technology officer John McKinley has been brought back as an interim measure.

Last month, AOL's own researchers posted the search requests and other data of 650,000 AOL subscribers on a research website. In total, the company revealed over 20m keyword searches. Their intention was good: to allow other search technology researchers to scrutinise traffic statistics and get a better understanding of what was being looked for and how the subsequent search results were used.

The data itself did not technically breach any privacy laws as it did not reveal the identity of the users themselves. Instead, they were referred to by unique user numbers. But the data did reveal details of what was being searched for, which could be used to work out who was doing the searching. The search data itself was full of personal information about other people.

Bloggers soon got wind of the AOL leak and by the time AOL decided that it was a bad idea to have so much information freely available to everyone, the data had been downloaded several hundred times, according to web experts.

Separately, Google saw its share of the lucrative US online search market dip last month, ending an 11-month run of market share gains. The company still dominated the market, capturing 43.7% of the 6.7bn online searches made by US web users. That performance was up 7.2% on the same month last year but down a percentage point on the market share it gained in June.

Yahoo! saw its share of the market increase slightly to 28.8% while Microsoft's MSN remained in third place at 12.8%. AOL, meanwhile, recorded a share of just 5.9%, meaning it has lost four percentage points over the past year.